you can order Hoffmans online...but the shipping comes into play there...I ordered 10 18 Qt bags this year and even with shipping, I came out better than buying it locally...here is a steal on it from Amazon...
http://www.amazon.com/Hoffman-30118-Seed-Starter-Quarts/dp/B000BPPP4U
I have tried the Fox Farms Light Warrior and was disappointed in the size of the perlite...large chunks that came to the top of the mix when I was loading it in the trays and even though the perlite holds water nicely, the chunks were too big and IMO made the roots grow around them...
Jimmy Seed Starting mix is my second choice...
you just want a very light weight soil-less mixture that holds water well and has zero nutrients in it...